The crystal lattice of a pharmaceutical salt is composed of ionized drug molecules and counter ions of opposite charge, which form a unique crystal structure. Since the physicochemical properties of a drug is dictated by the crystal structure, different salt forms of a drug exhibit different physicochemical properties such as melting point, crystallinity and hygroscopicity—factors which can ultimately affect the processability, bioavailability, and stability of the drug. Therefore it is valuable to prepare and characterize various salt forms. Having different forms to choose from provides new opportunities to improve the performance of a pharmaceutical product.
Pridopidine, i.e. 4-(3-methanesulfonyl-phenyl)-1-propyl-piperidine, is a drug substance currently in clinical development for the treatment of Huntington's disease. The hydrochloride salt of 4-(3-methanesulfonyl-phenyl)-1-propyl-piperidine and a method for its synthesis is described in WO 01/46145. In WO 2006/040155 an alternative method for the synthesis of 4-(3-methanesulfonyl-phenyl)-1-propyl-piperidine is described. In WO 2008/127188 N-oxide and/or di-N-oxide derivatives of certain dopamine receptor stabilizers/modulators are reported, including the 4-(3-methanesulfonyl-phenyl)-1-propyl-piperidine-1-oxide.